The invention is in the field of solar heating, and more particularly pertains to domestic hot water heating and storage using a normally completely passive flat plate collector system with built-in passive anti-reverse siphon features and anti-freeze-damage construction.
The parent patent to this application and its predecessors described and claimed various applications and modifications of an anti-reverse-siphon system using a passive anti-reverse-siphon loop, or "ARS" loop. Previously, unless there were an electrical or mechanical device to prevent back flow, the hot water tank had to be elevated above the flat plate collector so that when the collector cooled at night to well below the temperature in the hot water storage tank, the dense, cold water would settle to the bottom of the system, which would be the collector. If the tank were at the same height as the collector or lower than the top of the collector, the pressure head developed on a cold night by the cold water in the collector would overcome the pressure in the not-so-cold cold water supply line to the collector and cause the system to reverse-siphon, systematically drawing all of the previously heated water from the hot water tank through the collector and cooling it to ambient temperature before returning it to the tank. Obviously this was not desireable.
But by the device of the ARS loop, the tank can be at the same height as the collector, making it possible to integrate the collector and tank into more compact, efficient, easily installed and aesthetically pleasing packages than were possible when working within the constraint of having to have the tank above the collector.
The ARS loop basically comprises a downwardly concave loop that extends from a lower portion of the hot water storage tank up through the tank, exiting the tank through its top, passing up and then looping back down to define the cold water supply line for the flat plate collector. When the collector cools at night to temperatures well below the temperature in the tank, the collector panel will begin to backflow. But, with the ARS loop in place, the backflow will be essentially stopped because now the pressure head of the cold water in the collector panel supply line cannot dump directly into the bottom of the storage tank unimpeded, but must overcome the opposing pressure head developed by the hot water in the dip tube extending down into the hot water tank.